For some time, a general trend in development in wireless communications networks has been towards increasing transmission frequencies and increasing channel widths to enable increasing data rates to accommodate a continuing trend of using wireless devices of ever greater ranges of capability to exchange ever greater quantities of data. This trend has been seen among wireless wide area networks (WWANs), various variants of 3G and 4G cellular wireless networks, and wireless local area networks (WLANs).
With regard to WLANs, this trend can be observed in the development of the various 802.11 series standards promulgated by the Institute of Electrical and Electronics Engineers of New York, N.Y. over the last several years, including IEEE 802.11a/g, 802.11n, 802.11ac. However, in a recent shift, a new 802.11ah task group of the IEEE is currently developing a new variant of 802.11 series WLAN standard with comparatively lower data rates with narrower channels and transmissions at lower frequencies.
The lower transmission frequencies of 802.11ah are intended to enable greater range, and the narrower channels resulting in the lower data rates are meant to enable support for comparatively simpler and lower cost wireless devices that are unlikely to need to exchange relatively large quantities of data. An example of an intended use of 802.11ah includes enabling the provision of wireless arrays of sensors disposed about a building, a field, onboard vehicles, in traffic signals, on or in people (e.g., medical sensors), animals, etc. Such sensors are envisioned as detecting medical, intrusion, environmental/weather, power transmission/distribution, and other types of data and information, and conveying what is detected to other wireless devices in quantities of data that are generally expected to be relatively small.
Yet, it is also desired to simultaneously accommodate higher function wireless devices (e.g., smart phones, portable computers, etc.) exchanging larger quantities of data. However, the lower data rate of 802.11 ah is expected to result in any exchange of such larger quantities of data taking considerably longer than would be the case with many of the other 802.11 series standards. By way of example, an exchange of the typically larger sized data packet often observed in conveying images, audio, video, etc. between higher function devices via 802.11ah is expected to take 10's of milliseconds to accomplish.
Such lengthy transmission times to transmit a packet greatly increases vulnerability to signal degradation developing and worsening over the time required to complete its transmission. Such signal degradation arises from changing environmental conditions, and introduction of interference from transmission among other devices unrelated to network traffic. Signal degradation can also be caused by Doppler shift effects arising either from one wireless device moving at considerable speed relative to the other (e.g., a wireless device in a vehicle), or from a sizable object moving at considerable speed in the vicinity of the path of the signal between two wireless devices (e.g., a vehicle moving through the area).
Maintaining a high level of signal quality during the transmission of a packet has typically entailed embedding various features in the transmission of each packet, including a preamble that includes a known pattern of symbols to enable initial channel estimate, and the transmission of pilot signals with the packet to enable phase tracking and updates to channel estimate by a receiving wireless device. However, at least some of such features embedded in a transmission require some considerable processing ability (and an accompanying increase in use of electric power) on the part of a receiving wireless device to make use of them. Though such increased requirements may pose a minimal challenge to higher function wireless devices, lower cost wireless devices tend to be more limited in available processing ability and/or available electric power. It is with respect to these and other considerations that the embodiments described herein are needed.